Particulate matter detection device

Abstract

A particulate matter detection device that detects the diameter and the amount of particulates in exhaust gas while reducing detection error caused by deterioration such as the deterioration of electrodes is provided. In the particulate matter detection device, which measures particulates in a gaseous body, AC voltages having different frequencies are applied to a pair of electrodes disposed apart from each other. The resulting impedances to the different frequencies are detected. A resistance component and/or a capacitance component of the impedances to the different frequencies are calculated. The average diameter and/or the number of particulates in the gaseous body are estimated in accordance with changes in the resistance component and/or the capacitance component.

The invention claimed is: 
     
       1. A particulate matter detection device for measuring particulates in a gaseous body, the device comprising:
 frequency control means for controlling the frequency of an AC voltage applied to a pair of electrodes disposed apart from each other; 
 AC impedance detection means for detecting impedances to different frequencies when AC voltages having the different frequencies are applied; 
 component calculation means for calculating a resistance component and/or a capacitance component of the impedances to the different frequencies; and 
 particulate diameter estimation means for estimating the average diameter and/or the number of particulates in the gaseous body in accordance with changes in the resistance component and/or changes in the capacitance component. 
 
     
     
       2. The particulate matter detection device according to  claim 1 ,
 wherein, when calculating the resistance component and/or the capacitance component, which each include an intraparticle component and a particle boundary component, the component calculation means calculates the intraparticle component, which is attributable to the internal characteristics of particulates, and the particle boundary component, which is attributable to the interfacial characteristics between particulates, and 
 wherein the particulate diameter estimation means estimates the average diameter and/or the number of particulates in accordance with the result of comparison between the intraparticle component and the particle boundary component. 
 
     
     
       3. The particulate matter detection device according to  claim 2 , further comprising:
 particulate matter amount estimation means for estimating the amount of particulate matter in the gaseous body in accordance with the intraparticle component and the particle boundary component, which are included in the resistance component. 
 
     
     
       4. The particulate matter detection device according to  claim 2 , further comprising:
 inter-electrode resistance detection means for detecting the resistance between the electrodes; and 
 particulate matter amount estimation means for estimating the amount of particulate matter in the gaseous body in accordance with the detected inter-electrode resistance. 
 
     
     
       5. The particulate matter detection device according to  claim 4 , further comprising:
 saturation judgment means for judging whether the estimated particulate matter amount has reached a reference amount indicative of saturation, 
 wherein, when it is concluded that the particulate matter amount has reached the reference amount, the AC impedance detection means performs an impedance detection process. 
 
     
     
       6. The particulate matter detection device according to  claim 1 , further comprising:
 inter-electrode resistance detection means for detecting the resistance between the electrodes; and 
 particulate matter amount estimation means for estimating the amount of particulate matter in the gaseous body in accordance with the detected inter-electrode resistance. 
 
     
     
       7. The particulate matter detection device according to  claim 6 , further comprising:
 saturation judgment means for judging whether the estimated particulate matter amount has reached a reference amount indicative of saturation, 
 wherein, when it is concluded that the particulate matter amount has reached the reference amount, the AC impedance detection means performs an impedance detection process. 
 
     
     
       8. The particulate matter detection device according to  claim 1 , further comprising;
 particle resistance component calculation means for calculating a particle resistance component, included in the resistance component calculated by the component calculation means, attributable to the internal characteristics and interfacial characteristics of particulates, is distinguished from components attributable to the others; wherein, 
 the particulate matter estimation means estimates the amount of particulate matter in accordance with the particle resistance component. 
 
     
     
       9. A particulate matter detection device for measuring particulates in a gaseous body, the device comprising:
 a frequency controller that controls the frequency of an AC voltage applied to a pair of electrodes disposed apart from each other; 
 an AC impedance detector that detects impedances to different frequencies when AC voltages having the different frequencies are applied; 
 a component calculator that calculates a resistance component and/or a capacitance component of the impedances to the different frequencies; and 
 a particulate diameter estimator that estimates the average diameter and/or the number of particulates in the gaseous body in accordance with changes in the resistance component and/or changes in the capacitance component.